1. Field of the Invention
The invention relates to an apparatus and method for plastic extrusion. Specifically, the invention relates to a novel, improved apparatus and method for plastic extrusion, in which a transition portion and an upper polygonal groove integrally or separately provided on the entire inner surface of a transport section cylinder improves the processing ability and enables at least inert gas components and volatile components from a plastic to be removed through a hopper.
2. Description of the Related Art
JP-A-06-278192, as depicted in FIGS. 6 to 8, describes a gas removing structure of a related-art plastic extrusion apparatus.
Specifically, a twin screw extruder is indicated as reference 1 in FIG. 6. The twin screw extruder 1 has a cylinder 2 including a transport section cylinder 3, a kneading section cylinder 4, and a releasing section cylinder 5, which are arranged from an upstream side A towards a downstream side B.
The upstream side A of the cylinder 2 has a hopper 6 installed for supplying a plastic raw material P into the cylinder 1. The downstream side B of the hopper 6 of the cylinder 1 has an inner tube 81 of a degassing device 8 installed as a vent portion installed on a vent opening 7.
The degassing device 8 includes a devolatilization opening 9 and a header 10 of a spring urging type, which are configured to be able to open or close.
A pair of screws 11 is rotatably installed in the cylinder 1, and has a transport section screw 20, a kneading section screw 21 and a releasing section screw 22, from the upstream side A towards the downstream side B.
An extrusion process in which a plastic raw material P is kneaded by the twin screw extruder 1 will be described.
First, the plastic raw material P is supplied from the hopper 6 to the transport section cylinder 3 and is conveyed towards the downstream side of the twin screw extruder 1 by rotation of the screw 11. The conveyed plastic raw material P is plasticized, melted and kneaded by heat energy supplied from the cylinder 2, which may be heated and cooled, and by shear stress of the mixing section screw 21. When the plastic raw material P is supplied to the hopper 6, conveyed towards the downstream B of the extruder 1 by rotation of the screw 11, and plasticized, melted and kneaded by the kneading section cylinder 4, the kneading section cylinder 4 is fully charged with the molten plastic and then sealed. Then, kneaded air or inert gas components mixed with the plastic raw material P, volatile components remaining within the plastic raw material, etc, flow backwards to the side of the hopper 6 having lower pressure. These gas components are removed by the degassing device 8 because they compromise the conveying ability of the screw 11. At the same time, however, the degassing device 8 sucks a portion of the raw material. Since the sucked raw material is attached on the surface of the inner tube 81, the attached raw material is removed by force by means of shaking the inner tube 81 while knocking the header 10 with, for example, a manually-operated or motor-operated rammer or air knocker, before the raw material was carbonized.
The gas removal structure of the above-described related-art plastic extrusion apparatus has been exposed to the following drawbacks.
When a raw material is of a powder type and has a small particle diameter, or when the raw material contains a large amount of gas components, the powder escapes the inner tube of the degassing device and is removed, so that processing ability becomes deteriorated. Moreover, since the gas removal structure requires a vent portion, an intake source from an outside, such as a vacuum pump, becomes necessary in addition to accessory components including a motor or metallic parts of specific use. Thus, the cost of equipment is increased.
The invention is to solve the aforementioned problems. For example, the present invention may process a large ejection amount without compromising the processing ability even when a raw powder has a small particle diameter or contains a large amount of gas components.
According to one illustrative aspect of the invention, there is provided a plastic extrusion method comprising: preparing a cylinder comprising a transport section cylinder, a kneading section cylinder and a releasing section cylinder, wherein a screw is installed in the cylinder and comprises a transport section screw, a kneading section screw and a releasing section screw; supplying a plastic raw material into the cylinder from a hopper of a raw material supplying portion at an upstream side of a transport section cylinder; plasticizing and kneading the plastic raw material; and extruding the plasticized and kneaded material from the releasing section cylinder, wherein the transport section cylinder comprises an upper polygonal groove and a transition portion, the transition portion being arranged at the downstream side of the upper polygonal groove and being configured as a shape in which the upper polygonal groove gradually disappears, and wherein in the supplying the plastic raw material, the plastic extrusion method comprises releasing at least inert gas components and volatile components toward the hopper when the plastic raw material passes through the upper polygonal groove. The cylinder comprises no vent portion for releasing the inert gas components and volatile components to an outside. The upper polygonal groove comprises at least four grooves, and a depth H of the at least four grooves satisfies 0<H≦0.1 D, where D is the inner diameter of the cylinder. The screw is configured as twin screws. The screw is configured as twin screws turning inwards in different directions. The upper polygonal groove is provided in a separate upper polygonal cylinder. The upper polygonal groove and the transition portion are provided in a separate transition cylinder. The upper polygonal groove and the transition portion are integrally incorporated in the cylinder.
According to another illustrative aspect of the invention, there is provided a plastic extrusion apparatus for supplying a plastic raw material into a cylinder from a hopper of a raw material supplying portion at an upstream side of a transport section cylinder, for plasticizing and kneading the plastic raw material and for extruding the plasticized and kneaded material from a releasing section cylinder, wherein the cylinder comprises the transport section cylinder, a kneading section cylinder and the releasing section cylinder, wherein a screw is installed in the cylinder and comprises a transport section screw, a kneading section screw and a releasing section screw is installed in the cylinder, wherein the transport section cylinder comprises an upper polygonal groove and a transition portion, the transition portion being arranged at a downstream side of the upper polygonal groove and being configured as a shape in which the upper polygonal groove gradually disappears, and wherein the plastic extrusion apparatus is configured to release at least inert gas components and volatile components toward the hopper when the plastic raw material passes through the upper polygonal groove. The cylinder comprises no vent portion for releasing the inert gas components and volatile components to an outside. The upper polygonal groove comprises at least four grooves, and a depth H of the grooves satisfies 0<H≦0.1 D, where D is the inner diameter of the cylinder. The screw is configured as twin screws. The screw is configured as twin screws turning inwards in different directions. The upper polygonal groove is provided in a separate upper polygonal cylinder. The upper polygonal groove and the transition portion are provided in a separate transition cylinder. The upper polygonal groove and the transition portion are integrally incorporated in the cylinder.
A plastic extrusion method and apparatus according to the invention may have the following effects accomplished by the aforementioned structures.
Specifically, a plastic extrusion apparatus according to the invention is configured to supply a plastic raw material into a cylinder from a hopper of a raw material supplying portion at the upstream side of a transport section cylinder, to plasticize and knead the plastic raw material and to extrude the plasticized and kneaded material from a releasing section cylinder. The cylinder includes at least the transport section cylinder, a kneading section cylinder and the releasing section cylinder, and a screw including at least a transport section screw, a kneading section screw and a releasing section screw is installed in the cylinder. Furthermore, the transport section cylinder includes an upper polygonal groove and a transition portion, the transition portion being arranged at the downstream side of the upper polygonal groove and being configured as a shape in which the upper polygonal groove gradually disappears. When the plastic raw material passes through the upper polygonal groove, at least inert gas components and volatile components escape through the hopper to the outside. According thereto, a frictional coefficient increases in the cylinder inner surface by an upper polygonal groove formed on the inner surface of the transport section cylinder of the extruder, thereby increasing the driving force and subsequently the processing ability.
Furthermore, when a plastic raw material passes through the upper polygonal groove, the material enters, and is then compressed at, the polygonal-shaped groove portion of the upper polygonal groove, and an apparent volume density of the plastic raw material increases accordingly. Therefore, since inert gas components, kneaded air, volatile components remaining within the plastic raw material, etc, pass through the groove and efficiently move to the side of the hopper having a lower pressure, the apparatus prohibits gas from passing through a screw channel, thereby maintaining the conveying ability of the screw.
Also, since the cylinder does not require a vent portion therein, additional accessory device such as a vacuum pump for connecting with such a vent portion is not required at all. All that is required is to fabricate the inner wall of the cylinder. As such, the cost of additional equipment may be reduced with simplified maintenance and improved reliability achieved.
The upper polygonal groove is configured to include at least four grooves, and the depth of the grooves satisfies 0<H≦0.1 D, where D is the inner diameter of the cylinder. Therefore, a frictional coefficient in the cylinder inner wall may be sufficiently obtained as necessary.
The upper polygonal groove is configured in a separate upper polygonal cylinder. Therefore, the cylinder may be easily manufactured, and an upper polygonal cylinder may be so made as to have different frictional coefficients by the kind of a raw material.
Moreover, the upper polygonal groove and the transition portion are configured in a separate transition cylinder. Therefore, the cylinder may be easily manufactured, and a transition cylinder may be so made as to have different frictional coefficients by the kind of a raw material.
Furthermore, the upper polygonal groove and the transition portion are integrally configured in a cylinder. Therefore, the upper polygonal groove and the transition portion are manufactured integrally with the transport section cylinder, and the cost of process may be reduced accordingly.